1. Field of the Invention
This invention relates to a computer-aided product design system, more specifically, a product design system constituted as the so-called CAD (computer-aided design)/CAM (computer-aided manufacturing), CIM (computer-integrated manufacturing) and other product design systems.
2. Description of the Related Art
The technology taught by Japanese Laid-Open Patent Application Hei 9-319,772 can be given as an example of this kind of computer-aided product design system. In this prior-art, the features of the product shape are determined in the preceding product design process, thus facilitating automated design of the upper mold shape in the mold design process in the subsequent process, whereby shortening of the period of time to design in both processes is possible.
In CAD/CAM or CIM, when molds are used to manufacture products, the designer (engineer) normally uses a CAD system to first make or design a product model or product shape from a geometric model such as a solid model obtained by sweeping a primitive (a basic elements such as a circular cylinder, a cube) on the screen to conduct Boolean set operations to combine the primitives and the product model is then used to make or design a mold model in the mold design process. Next, this mold model is used to make mold fabrication data, after which the mold is fabricated by CNC (computer numerical control) fabrication, etc., using the data, and the fabricated mold is used to make the product by casting or cutting.
In this way, the shape of the product model constructed in the product design process determines the shape of the product, and therefore the release draft, i.e., the release draft for releasing the product from the mold required for the casting process, must be added to the product model in the product design process. A rounded portion referred to as a fillet is applied or formed on a square edge in this product model. Specifically, the product model is edited such that portions where two lines or curves intersect continue smoothly with a circular arc (fillet) having designated or specified radius of curvature.
After the geometric model such as the solid model has been completed to a desired shape with surfaces adjoined tangentially continuous by a fillet, there may be a need to change a portion of the model shape for a reason that the release draft is insufficient or the thickness is to be changed. In the prior art product design process using CAD/CAM or CIM, however, once the model has been completed, it has been impossible to change a portion of the model while maintaining the surfaces adjoined to be tangentially continuous, in other words, it is impossible to change a portion of the model while enabling to use the definition of shape before change.
Even in the prior art, it is possible to change the color of surfaces (‘adjoined to be tangentially continuous by fillets) in the model to be different from each other as illustrated in FIG. 13. It should be noted here that the difference of colors are expressed by the difference in lines or hatching. It is also possible, even in the prior art, to extract or separate the surface element (face) from the model as illustrated in FIG. 14. Even in the prior art, thus, it is possible to recognize the boundary adjoining the surfaces. However, in the prior art, it is not possible to change a shape of the model while enabling to use the definition of shape obtained before the shape has been changed.
This will be specifically explained with reference to FIG. 15. In a solid model of a circular cylinder having a rounded side surface indicated by A, B, C, suppose that A and C are adjoined by a fillet B, in other words, A, B and C are not independent from each-other and hence, A is a portion of surface. In the illustrated example, if A is to be increased (changed) to An, since a step (level difference) arises between An and C, a line lac connecting An and C must be drawn from the edge (immediately before the step), which makes it impossible to use the definition of shape before change and is restrictive. Needless to say, if the definition of shape for An is newly calculated (i.e., data after change), the line lac will be easily drawn by using the new data for An together with the original data for C. However, re-calculation of the definition of shape is tedious and degrades the efficiency of product design.